1. Field of the Invention
The present invention relates to a developing device, a processing cartridge, and an image forming apparatus.
2. Description of the Related Art
Contact developing methods and non-contact developing methods are widely known as currently used developing methods employing monocomponent toner. Specifically, (1) a contact developing method employing a developing roller having an elastic layer, (2) a non-contact developing method with a magnetic toner employing a metal sleeve, and so forth, have been proposed. Regarding these developing methods, several measures have been proposed for a toner regulation member for the purpose of forming a thin layer of monocomponent toner on a developer bearing member.
(1) Contact Developing Method Employing Developing Roller Having Elastic Layer (FIG. 8)
A developing method is well known wherein developing is performed by bearing a non-magnetic developer on a developing roller 3, which is an elastic roller having a dielectric layer, and causing the developer to make contact with the surface of a photosensitive drum 1. Supplying the developer to the developing roller 3 is performed by a supply roller 5, which makes contact with the developing roller 3. The supply roller 5 has a function for transporting the developer from within a developer container T and adhering this to the developing roller 3, as well as removing the developer remaining on the developing roller 3 before subsequent processing.
Layer regulation of the developer adhered to the developing roller 3 and frictional charge applied thereto are performed by causing a toner regulation member 4c to make contact with the developing roller 3. A regulation member has been proposed which supports one end side 4c1 of a metal thin plate serving as the toner regulation member 4c, and wherein the underside of the other end side 4c2 makes contact with the developing roller 3. The electrostatic image formed on the photosensitive drum 1 is developed by the developer coated on the developing roller 3 by the toner regulation member 4c. 
(2) Non-Contact Developing Method With Magnetic Toner Employing Metal Sleeve (FIG. 14)
A non-contact developing method employing a monocomponent toner is widely known, which is performed by employing a cylindrical developing sleeve 3a, and the layer regulation of the developer and the frictional charge applied thereto are performed by causing the toner regulation member 4d to make contact with the developing sleeve 3a. Supplying the developer to the developing sleeve 3a is performed magnetically by providing a magnet within the developing sleeve 3a. 
A DC bias and an AC bias are applied between the developing sleeve 3a and a photosensitive drum 1, and developing is performed in a non-contact manner. Even if there is too much toner on the developing sleeve 3a with insufficient charge, unnecessary toner development can be suppressed by disposing a magnetic pole in the vicinity of the developing unit. Thus, Japanese Patent Laid-Open No. 02-025866 proposes that the charge amount of the developer on the developing sleeve 3a can be set so as to be relatively low, and the toner regulation member 4d employs a rubber plate with low contact pressure with consideration for the stability of contact.
However, in the case of employing a blade-shaped toner regulation member with the contact development method (1), a configuration is made wherein a thin elastic member is supported along one side in the longitudinal direction thereof, and the underside of the facing portion thereof makes contact with the developing roller. Accordingly, there has been the problem wherein creating a smaller apparatus has been difficult. That is to say, if the size of the toner regulation member is reduced, the distance between the point of support wherein one side of the thin elastic member is supported, and the point of contact with the developing roller, i.e. the free length, becomes shorter. Thus, the spring constant of the contact pressure increases, and even if the setting position of the toner regulation member varies only a small amount, the contact pressure varies widely. Therefore, highly precise assembly has been necessary in order to set a stable contact pressure.
Also, reduction in length of the free length of the thin elastic member tends to increase the effects of uneven adhesion at the one-side supporting portion, and the difficulty in applying even pressure over the entire lengthwise direction adds to the difficulty in creating a smaller apparatus.
Also, with the non-contact developing method (2) with a magnetic toner, a rubber sheet supported along one side in the longitudinal direction is employed as the toner regulation member. When the state of the rubber sheet is maintained for a long period of time in a deformed shape, it becomes difficult to return the rubber to the shape thereof prior to deforming, whereby so-called creeping occurs. When creeping occurs, the contact pressure varies, and so obtaining a stable contact pressure for a long period of time has been difficult. It has been found desirable to provide for a solution to the above-mentioned problems.